For testing and diagnostic purposes, it is at times useful to determine the fluorescence of the aqueous humor which is in the anterior chamber between the cornea and the lens of the eye. For example, such a determination can be used to test the effectiveness of anti-glaucoma therapeutics, to test the bioavailability of drugs and to test for the inflammatory response.
The shape of the normal eye is maintained by an internal fluid pressure of about 15 millimeters of mercury. That intraocular pressure (IOP) is controlled by the balance of flow of aqueous humor due to secretion from and filtration through the ciliary body and drainage through the trabecular meshwork. In the disease of glaucoma, the balance is disturbed. The result is an increase in IOP which eventually damages the optic nerve and causes blindness.
Aqueous humor is a watery fluid produced by the ciliary body in the posterior chamber behind the iris. Aqueous humor then flows through the pupil and the anterior chamber and drains through the trabecular meshwork. The IOP increases when the resistance to flow through the trabecular meshwork is great relative to the amount of aqueous humor which is produced. Some drugs used to treat glaucoma reduce the rate of formation of aqueous humor.
Aqueous fluorophotometry is a method used to observe the flow rate of aqueous humor through the anterior chamber of the eye. Such observations are important in understanding the pathophysiology of glaucoma and the mechanics underlying the effects of antiglaucomatous drugs. According to this method, a fluorescent dye is instilled into the anterior chamber. This may be accomplished by placing a drop of aqueous dye on the cornea; the fluorescent dye passes through the cornea into the anterior chamber. The changing concentration of the fluorescent dye in the anterior chamber is directly related to the flow rate of aqueous humor. The concentration of the dye has in the past been determined by projecting light into the anterior chamber using a slit lamp and detecting the resultant corneal and aqueous fluorescence. In such systems, only about one part in a billion of the light leaving the projection lamp is detected. Accordingly, expensive photomultiplier light measurement systems have been used and the systems have suffered fairly large measurement errors. Further, where the dye is instilled into the anterior chamber through the blood, the iris behind the anterior chamber can be fluorescent, and that fluorescence can interfere with the measurements.
In addition to testing for the flow of aqueous humor, aqueous fluorophotometry can be used to judge the bioavailability of drugs and the inflammatory response. The bioavailability of a drug is the ability of that drug to penetrate into the eye. By placing a fluorescent tag on the drug and applying it to the eye, the aqueous fluorescence is an indication of the degree of penetration of the drug into the anterior chamber.
During the inflammatory response of a body, large fluorescent molecules injected into the blood are more likely to penetrate the walls of the blood vessels and enter the anterior chamber. A large amount of fluorescent molecules in the anterior chamber indicates a significant inflammatory response which in turns indicates a significant inflammation. A test for aqueous fluorescence can be used diagnostically to determine whether there is an inflammation and therapeutically to determine the response of the body to treatment. In the past, the inflammatory response has been measured by observing the scattering of light by white blood cells and large protein molecules which pass from the blood vessels into the anterior chamber. A more efficient aqueous fluorophotometry test will provide a quantitative and objective test which has not heretofore been available.